This invention relates to the field of head suspended ear covering apparatus usable for both protection against high intensity ambient noise and two way communication with the protected user subject.
Persons obligated to work in high ambient noise enviroments have been known to incur premature hearing loss and other medically abnormal conditions. The metal fabrication industries, certain construction work, sawmill operation, riveting, and certain types of mineral mining provide notable historical examples of work environments in which hearing loss has resulted from prolonged exposure to impact and other high-energy noises. In more recent times, persons working in close proximity to running aircraft engines, in electrical power generation plants, and as crew members in the gunnery turrets of naval vessels and armored tanks, may be exposed to undesirable levels of sound energy and, without the use of protective equipment, become susceptible to noise-induced physiological problems. In relatively recent times, the advent of occupational safety and health administrations (OSHA) at both the federal and state government levels, has increased the awareness and knowledge needed in preventing prolonged exposure to undesirable ambient noise. The OSHA espoused rules relating noise exposure time inversely with noise intensity have been particularly effective in reducing the incident of work-related hearing difficulties.
The new awareness, together with worker preference for convenient, lightweight and reliable hearing protection apparatus and the inherent requirements for a protected worker to communicate with other persons in his enviroment, has created a need for improvements in the hearing protection/communications equipment art. An opportunity for well-considered simple and rugged equipment of this type is clearly illustrated by the working environment of a military ground crew member in the aircraft maintenance arrival and departure operations of a U.S. Air Force base.
In this environment there is often a requirement for a ground crew member, positioned on the outside of an aircraft with a running engine to have the benefit of both ear-defending ambient noise protection and communication with pilot or other crew-members stationed inside the fuselage of the aircraft. In a slight variation of the scenario, a ground crew member can expect to need hearing protection without needing to converse with the aircraft crew. Such needs often occur where the aircraft of interest is in motion or where ear protection is needed from the sound generated by adjacent aircraft, or where power tools such as air driven drills or racheting devices must be used in the confined spaces of an aircraft. Since the need transition from simple ear protection to ear protection combined with communications capability can be expected to occur frequently and on short notice in the activities of ground crew personnel. It is desirable to provide such persons with a single piece of headset equipment that is capable of performing both the ear protecting and communications functions with reasonable efficiency. In the interest of assuring optimum ear protection and desirable headband characteristics as discussed below herein, the preferred equipment for such usage is in the nature of ear protection that is also provided with communications capability rather than communications apparatus that is used secondarily for ear protection.
In the Air force ground crew environment, experience has shown that operating lifetime and ability to withstand hard usage are especially demanding additional requirements for headset equipment. In the ground crew environment, hostile events in the nature of inclement weather conditions, headset droppage or other physical abuse, atmospheric dust and dirt and intense subjection to human body by-products such as moisture, salt, and organic oils, are expected headset operating life considerations. The prospect of droppage and other abuses is particularly great for equipment of this type. Such physical abuse and the other hostile conditions encountered frequently impose repeated repair requirements and general unreliability as expected attendants of using heretofore available headset equipment.
The oldest headset microphone that is still in wide use is known as the H-133c/AIC of which most were manufactured by the David Clark Company. It was bulky in construction, and had numerous wires exposed that were prone to damage. Additionally the earcup transducers were attached using annular ring assembly that often came loose, allowing the transducers to fall out of the earcup and the electrical connections to the transducers to sever and fail. The device had a microphone inside of a shield, commonly called a mic-muff. This mic-muff was attached to the earcups by straps and hardware which often failed, causing the operator to manually hold the mic-muff to his face. The H-133c/AIC was later banned for use by U.S. Air Force due to an unacceptible leakage of 2800 Hz.
The second headset microphone is the one that is most familiar to military aircrew members, the H-157/AIC manufactured by Astrocom Electronics Inc. The device was designed as a light weight communications headset not for use in a hazardous noise enviroment. It had an external boom-mounted microphone that was infamous for coming loose at the boom to earcup attachment point. The transducers inside the earcup came loose frequently, causing the electrical connections to fail. The device had a short life-span due to electrical connections failing, both to the transducers and at the electrical tether used to connect the headset to the headset.
An improved version of the H-157/AIC model is the H-157a/AIC. It has better hardware attaching the microphone boom to the earcup. However, it retained the inherent electrical failure flaws and can only be used in low to medium noise levels. The manufacturers are Astrocom Electronics Inc. and Roanwell Corporation.
With failure of the H-133c/AIC to protect the wearer due to the 2800 Hz leakage a new milspec emerged; the M7819/1-01-Manufactured by the David Clark Co. and Astrocom Electronics Inc. To eliminate the 2800 Hz leak the wires going into the earcups thru a rubber grommet have been replaced by a one piece wire harness that utilizes a molded plug with flanges that effectively seal the interior of the earcup from outside noise and all frequencies. At first this device was plagued by open circuits due to wear and tear inside the harness assembly. For the most part the wiring harnesses have been beefed up eliminating internal open circuits of the wiring harness. However, the transducers were frequently coming out of the earcups. This was due to them being held inside of the earcups by a cheap grade of acoustic foam. The result was failed electrical connections. The most notable problem this headset has is found at high noise levels, the ambient noise bleeds into the mic-muff. This noise and the operator yelling in the device causes excessive noise exposure to those personnel on the receiving end of the transmission. This type of headset is encumbered by an obtrusive mic-muff and a permanently attached tether cord.
My Pat. No. 4,771,454 headset was designed for medium noise levels and for rugged use. It utilized riveting a metal ring to the earcup to hold the transducer in place with no possible way for it to come loose and fail electrically. To ensure the electrical integrity of the tether, a provision to disconnect it from the earcup when the device is used as an eardefender was incorporated. Originally connections in and out of the earcups passed thru rubber grommets. Theoretically, a possibility of the 2800 Hz leak existed, the device was upgraded to the M87819/1-01 specs. However, the device did not pass the intelligibility test (with upgrading) at the 115 dB level, as tested by the U.S. Air Force.
After receiving the results of the test preformed on Pat. No. 4,771,454, I decided to invent a new type of communications headset that was unencumbered in design and usable in very high noise environments. To do this I would have to eliminate externally mounted appendage type microphone and increase the foam thickness in the earcup cavity. The later increases hearing protection to the user. This criterion revealed a need for a new type of microphone transducer and an unconventional location for this microphone. In a moment of insight I remembered an article concerning a device called an ear-mic. This device was both a speaker and microphone in a small earplug package. It was at that time I conceived the idea mount the ear-mics inside the earcups in such a manner that they would automatically be inserted into the user's ears when the invention was donned. I then proceeded with the construction and testing of the invention to prove its feasibility.